U.S. patent number 7,723,249 [Application Number 11/520,043] was granted by the patent office on 2010-05-25 for ceramic material for high temperature service.
This patent grant is currently assigned to Sulzer Metco (US), Inc.. Invention is credited to Jacobus C. Doesburg, Mitchell Dorfman, Liangde Xie.
United States Patent |
7,723,249 |
Doesburg , et al. |
May 25, 2010 |
Ceramic material for high temperature service
Abstract
The invention is directed to a ceramic material for use in
thermal barriers for high temperature cycling applications and high
temperature abradable coatings. The material is an alloy formed
predominantly from ultra-pure zirconia (ZrO.sub.2) and/or hafnia
(HfO.sub.2) that has uncharacteristically high sintering resistance
to achieve a high service lifetime and low thermal conductivity to
achieve high operating temperatures. In the material, oxide
impurities such as soda (Na.sub.2O), silica (SiO.sub.2), alumina
(Al.sub.2O.sub.3), titania (TiO.sub.2), hematite (Fe.sub.2O.sub.3),
calcia (CaO), and magnesia (MgO) make up no more than 0.15 weight
percent. The invention provides materials to produce a coating
structure so that the changes in the coating microstructure over
the in-service lifetime are either limited or beneficial.
Inventors: |
Doesburg; Jacobus C. (Edmonton,
CA), Xie; Liangde (Pearl River, NY), Dorfman;
Mitchell (Smithtown, NY) |
Assignee: |
Sulzer Metco (US), Inc.
(Westbury, NY)
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Family
ID: |
37689568 |
Appl.
No.: |
11/520,043 |
Filed: |
September 13, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100075147 A1 |
Mar 25, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60724268 |
Oct 7, 2005 |
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Current U.S.
Class: |
501/103; 428/702;
428/701; 428/325 |
Current CPC
Class: |
C23C
14/083 (20130101); F01D 5/288 (20130101); C04B
35/486 (20130101); C23C 30/00 (20130101); C23C
4/11 (20160101); C04B 2235/3246 (20130101); Y10T
428/12618 (20150115); Y10T 428/24 (20150115); Y10T
428/12667 (20150115); Y02T 50/67 (20130101); Y02T
50/60 (20130101); C04B 2235/3227 (20130101); C04B
2235/3224 (20130101); Y10T 428/26 (20150115); C04B
2235/72 (20130101); Y10T 428/2982 (20150115); Y10T
428/24997 (20150401); Y02T 50/6765 (20180501); C04B
2235/3225 (20130101); Y10T 428/12611 (20150115); Y10T
428/24471 (20150115); Y10T 428/252 (20150115); Y02T
50/672 (20130101); Y10T 428/25 (20150115) |
Current International
Class: |
C04B
35/486 (20060101); C04B 35/488 (20060101); B32B
18/00 (20060101) |
Field of
Search: |
;501/103
;428/325,633,697,701,702,134,656,655,660 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
European Search Report date Feb. 14, 2007 for European Patent
Application No. 06121639.6. cited by other .
R. Va.beta.en, N. Czech, W. Mallener, W. Stamm, D. Stover,
"Influence of impurity content and porosity of plasma-sprayed
yttria-stabilized zirconia layers on the sintering behaviour", pp.
135-140, Apr. 10, 2000, www.eisevier.nl/locate/surfcoat, Germany.
cited by other .
Robert A. Miller, "Thermal Barrier Coatings for Aircraft
Engines--History and Directions", NASA Lewis Research Center Mar.
1995, pp. 17-27, Cleveland, OH. cited by other .
Lou George, "PRAXAIR Introduces New Yttria-Stabilized Zirconia
Powder", p. 22, www.ptihome.com, Spraytime First Quarter 2003.
cited by other .
"Amperit Thermal Spray Powder Catalog," H.C. Starck GmbH, published
2005. cited by other .
Online Catalog "Product Information Amperit 832 Catalog," H.C.
Starck GmbH, at
http://www.hcstarck.com/medien/dokumente/document.sub.--Produkti-
nfo832.pdf. cited by other .
"Amperit Thermal Spray Powder Catalog," H.C. Starck, published
1995. cited by other.
|
Primary Examiner: Group; Karl E
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 U.S.C. .sctn.119(e) from
U.S. Provisional Patent Application No. 60/724,268, filed on Oct.
7, 2005, which is incorporated herein by reference.
Claims
We claim:
1. A ceramic material for use in high-temperature thermal barriers
or abradable seal coatings, the ceramic material is supplied in a
form for thermal spray applications and comprises: about 4 to 20
weight percent of a stabilizer of one or more rare earth oxides;
and a balance of at least one of zirconia (ZrO.sub.2), hafnia
(HfO.sub.2) and combinations thereof, wherein the zirconia
(ZrO.sub.2) and/or hafnia (HfO.sub.2) is partially stabilized by
the stabilizer, wherein the total amount of impurities is less than
or equal to 0.15 weight percent, and wherein the amount of oxide
impurities is less than or equal to: about 0.01 weight percent
soda, about 0.01 weight percent silica, about 0.01 weight percent
alumina, about 0.01 weight percent titania, about 0.01 weight
percent hematite, about 0.025 weight percent calcia, and about
0.025 weight percent magnesia.
2. The ceramic material of claim 1, wherein the stabilizer is about
4-12 weight percent yttria.
3. The ceramic material of claim 1, wherein the stabilizer is about
6-9 weight percent yttria.
4. The ceramic material of claim 1, wherein the material is
supplied in the form of a chemical solution.
5. The ceramic material of claim 1, wherein the material is
supplied in the form of one of a powder or a slurry of partially
stabilized powder.
6. The ceramic material of claim 5, wherein the powder is a spray
dried powder of the individual constituents with an organic binder,
a spray dried powder of the combined constituents with organic
binder, a fused and crushed powder, an agglomerated and sintered
powder, a plasma densified material, or powder made from a chemical
solution.
7. The ceramic material of claim 5, wherein the powder material has
a particle size of about 5-150 microns.
8. The ceramic material of claim 1, wherein the total amount of
impurities is less than or equal to 0.10 weight percent.
9. The ceramic material of claim 1, wherein the ceramic material is
part of a blended ceramic material for use in high-temperature
thermal barriers or abradable seal coatings, the blended ceramic
material being supplied in the form of one of a powder or a slurry
of partially stabilized powder.
10. The ceramic material of claim 9, wherein the blended material
includes a placeholder.
11. The ceramic material of claim 10, wherein the one or more
ceramic materials comprises about 70-99 weight percent of the
blended material and the placeholder comprises about 1-30 weight
percent of the blended material.
12. The ceramic material of claim 1, wherein the stabilizer is
about 10-16 weight percent ytterbia.
13. The ceramic material of claim 1, wherein the stabilizer is
about 4-16 weight percent of a combination of yttria and
ytterbia.
14. The ceramic material of claim 1, wherein the stabilizer is
about 4-16 weight percent dysprosia.
15. The ceramic material of claim 1, wherein the stabilizer is
neodymia or europia or combinations thereof.
16. The ceramic material of claim 1, wherein the total stabilizer
is 4-16 weight percent and includes a primary stabilizer of yttria
and/or ytterbia and a secondary stabilizer of one or more other
rare earth oxides.
17. The ceramic material of claim 1, wherein the total stabilizer
is 4-16 weight percent and includes a primary stabilizer of
dysprosia and a secondary stabilizer of one or more other rare
earth oxides.
18. The ceramic material of claim 1, wherein the total stabilizer
is 4-20 weight percent and includes a primary stabilizer of yttria
and/or ytterbia and a secondary stabilizer of neodymia and/or
europia and combinations thereof.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A "MICROFICHE APPENDIX"
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to ceramic materials for thermal barriers and
abradable coating systems in high temperature and high temperature
cycling applications, and more particularly to ultra-pure zirconia
materials for use in thermal barrier and abradable coating
applications.
2. Description of the Related Art
Superior high-temperature properties are required to improve the
performance of heat resistant and corrosion resistant members.
These members include, for example gas turbine blades, combustor
cans, ducting and nozzle guide vanes in combustion turbines and
combined cycle power plants. Turbine blades are driven by hot
gasses, and the efficiency of the gas turbine increases with the
rise in operational temperature. The demand for continued
improvement in efficiency has driven the system designers to
specify increasingly higher turbine operating temperatures. Thus,
there is a continuing need for materials that can achieve higher
operational temperatures.
Thermal barrier coatings are used to insulate components, such as
those in a gas turbine, operating at elevated temperatures. Thermal
barriers allow increased operating temperature of gas turbines by
protecting the coated part (or substrate) from direct exposure to
the operating environment. An important consideration in the design
of a thermal barrier is that the coating be a ceramic material
having a crystalline structure containing beneficial cracks and
voids, imparting strain tolerance. If there were no cracks in the
coating, the thermal barrier would not function, because the
differences in thermal expansion between the metal substrate system
and the coating will cause interfacial stresses upon thermal
cycling that are greater than the bond strength between them. By
the creation of a crack network into the coating, a stress relief
mechanism is introduced that allows the coating to survive numerous
thermal cycles. Repeating crack networks are typically imparted
into the coating on varying space scales by manipulating the
thermodynamic and kinetic conditions of the manufacturing method,
and different structures known to perform the coating task have
been optimized likewise. In addition to this, cracks are also
formed during service, so the structure formed upon coating
manufacture changes with time, depending on the starting material
phases in the manufactured coating and thermal conditions during
service.
Another design factor determining coating lifetime is the sintering
rate of the coating. When the coating is cycled above half of its
absolute melting temperature, the coating begins to sinter causing
volume shrinkage. As the coating shrinks, the stress difference
between the coating and substrate increases. At a certain amount of
shrinkage (which varies depending on the type of structure and
thermal conditions during service), the stress difference exceeds
the bonding strength of the coating and it becomes detached.
Decreasing the sintering rate of the thermal barrier increases the
amount of time before the catastrophic shrinkage is experienced, so
it can become a major design consideration. For high purity
zirconia alloys, the onset of sintering commences at temperatures
above 1000.degree. C.
Historically, high temperature thermal barrier coatings have been
based on alloys of zirconia. Hafnia may also be employed due to its
chemical similarity to zirconia, but is generally cost-prohibitive.
Hafnia also is typically present in most zirconia materials in more
than trace amounts due to difficulty in separating the two oxides.
Zirconia and/or hafnia have the following combination of desirable
properties that other known ceramic systems do not possesses for
the application. First, zirconia alloys have some of the highest
melting points of all ceramics, and this means theoretically some
of the highest temperatures for which the onset of sintering
occurs. Second, zirconia alloys have one of the lowest thermal
conductivities of all ceramics. Third, zirconia has one of the
highest coefficients of thermal expansion of all ceramics, so it is
most compatible with transition metal alloys during thermal
cycling.
Zirconia alone cannot fulfill the coating requirements because it
undergoes a phase transformation from tetragonal to monoclinic
during thermal cycling. This transformation is presumed to cause a
detrimental volume change resulting in large strain differences
between the coating and the substrate. When the resulting stresses
exceed the bond strength of the coating to the substrate, the
coating will detach. For this reason a phase stabilizer is added to
the zirconia and/or hafnia, such as yttria, which suppresses the
tetragonal to monoclinic phase transformation.
Thermal spray abradable coatings are commonly used in gas turbine
applications. Abradable coatings are designed to preferentially
abrade when contact is made with a mating part. These coatings have
low structural integrity so they are readily abraded when they come
into contact with a moving surface with higher structural integrity
(such as the blade of a turbine). The coatings are designed so as
not to damage the mating surface. In many applications abradable
coatings are subject to the same thermal cycling conditions as the
thermal barriers described above. Thus, there is a continuing need
for materials suitable for abradable coatings that can achieve
higher operational temperatures.
Some previous efforts to improve coating life have focused on the
coating material and microstructure upon entry into service.
However, the heat cycle of in service parts also causes cracks
throughout the service life of the part. Thus, the microstructure
formed upon coating manufacture changes with time, depending on the
starting material phases in the manufactured coating and thermal
conditions during service. Because a consistent optimal crack
network is not typically maintainable throughout the service life
of the part, coating lifetime is ultimately determined by the
material selection and its manufacturing process. There remains a
need in the art for a coating material, coating material
manufacturing method, and coating manufacturing method that address
the changes in the coating microstructure during its service
lifetime.
SUMMARY
Accordingly, the invention is directed to a ceramic material for
use in thermal barriers for high temperature cycling applications
and high temperature abradable coatings. The material is an alloy
formed predominantly from ultra-pure stabilized zirconia
(ZrO.sub.2) and/or hafnia (HfO.sub.2) alloys that have
uncharacteristically high sintering resistance to achieve a high
service lifetime. The invention provides a desired coating material
so that the changes in the coating microstructure over the
in-service lifetime are retarded.
The limits for impurities discovered to decrease sintering rate and
therefore increase service lifetime compared with current impurity
concentrations when used as a coating and partially stabilized with
a rare earth oxide, for example, yttria (Y.sub.2O.sub.3) and/or
ytterbia (Yb.sub.2O.sub.5), are disclosed herein. Oxide impurities
are defined as materials which, when combined with each other or
with zirconia and/or hafnia, form phases with melting points much
lower than that of pure zirconia and/or hafnia.
In one aspect, the invention provides a ceramic material for use in
high-temperature thermal barriers or abradable seal coatings. The
said material has about 4 to 20 weight percent of a stabilizer of
one or more rare earth oxides; and a balance of at least one of
zirconia (ZrO.sub.2), hafnia (HfO.sub.2) and combinations thereof,
wherein the zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) is
partially stabilized by the stabilizer, and wherein the total
amount of impurities is less than or equal to 0.15 weight
percent.
In another aspect of the invention a blended ceramic material of
one or more ceramic materials is provided. Each of the ceramic
materials is for use in high-temperature thermal barriers or
abradable seal coatings and is supplied in the form of one of a
powder or a slurry of partially stabilized powder. Each of the
ceramic materials has about 4 to 20 weight percent of a stabilizer
of one or more rare earth oxides and a balance of at least one of
zirconia (ZrO.sub.2), hafnia (HfO.sub.2) and combinations thereof,
wherein the zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) is
partially stabilized by the stabilizer, and wherein the total
amount of impurities of the blended ceramic material is less than
or equal to 0.15 weight percent. Additional ceramic materials or
placeholder materials may also be included in the blended
material.
Conventional approaches to improving coating life-cycles have
focused on adding stabilizers to the base ceramic material. The
approach of the present invention provides previously unexpected
results in sintering data by identifying low-impurity materials.
When looking at the sintering data, changing the amount of
impurities slightly has a much greater effect on performance
compared with changing the amount and types of stabilizers.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide further
understanding of the invention and are incorporated in and
constitute a part of this specification. The accompanying drawings
illustrate embodiments of the invention and together with the
description serve to explain the principles of the invention. In
the figures:
FIG. 1 illustrates a perspective view of a turbine blade coated
with a thermal barrier of ceramic material;
FIG. 2 provides a graph showing the effect of impurities on the
sintering rates;
FIG. 3 provides a phase diagram for ZrO.sub.2;
FIG. 4 provides a standard phase diagram for stabilized ZrO.sub.2
showing the general alloying trends for various stabilizers
[Ceramic Phase Diagram, Volume 4, Fig 05241]; and
FIG. 5 provides a phase diagram for ZrO.sub.2 with stabilizer.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to the preferred embodiments
of the invention, examples of which are illustrated in the
accompanying drawings.
In an exemplary use of a material of the invention, FIG. 1 shows
one component of a turbine. Turbine blade 100 has a leading edge
102 and an airfoil section 104, against which hot combustion gases
are directed during operation of the turbine, and which undergoes
severe thermal stresses, oxidation and corrosion. A root end 106 of
the blade anchors the blade 100. Venting passages 108 may be
included through the blade 100 to allow cooling air to transfer
heat from the blade 100. The blade 100 can be made from a high
temperature resistant material. The surface of the blade 100 is
coated with a thermal barrier coating 110 made of ultra-pure
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) alloys in accordance
with the invention. The thermal barrier coating 110 may be applied
on, for example, a MCrAlY bonding layer with an alumina scale (not
shown) applied between the blade surface and the coating 110. The
coating 110 may be applied onto the bond coating surface through a
variety of methods known in the art including thermal spray
techniques such as powder flame spray and plasma spray and vapor
deposition methods such as electron beam physical vapor deposition
(EBPVD), high speed physical vapor deposition and low pressure
plasma spraying (LPPS).
When applied, the coating 110 contains a crack network that allows
it to survive the stress of numerous thermal cycles. As described
in the above background section, the crack network is altered to a
less desirable state by sintering and temperature cycling during
service. Thus the structure formed upon coating manufacture changes
with time, the rate depending on the starting material phases.
Decreasing the sintering rate increases the amount of time before
the closing of microcracks and creation of massive cracks,
increasing coating lifetime.
A dominant factor affecting sintering is the presence of specific
impurity phases within the structure made up of oxides which when
combined with each other or the zirconia alloy result in melting
points hundreds of degrees lower than that of the zirconia alloy
itself. These impurity oxides increase the sintering rate. FIG. 2
shows the effect of impurity on the sintering rate.
In one embodiment of the present invention, the material contains
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) partially stabilized
by a total of 4 to 20 weight percent of one or more rare earth
oxides having total impurities less than or equal to 0.15 weight
percent, and preferably less than or equal to 0.1 weight percent.
For purposes of the invention, rare earth oxides can be defined as
any oxide from group IIIB (column 3) of the periodic table of
elements, which includes scandia (Sc.sub.2O.sub.3), yttria
(Y.sub.2O.sub.3), lanthanide oxides and actinide oxides.
The material of the present invention contains zirconia (ZrO.sub.2)
and/or hafnia (HfO.sub.2) partially stabilized by a total of 4 to
20 weight percent of a primary stabilizing oxide such as ytterbia
and/or yttria, (and optionally additional stabilizers of one or
more rare earth oxides) having total impurities less than or equal
to 0.15 weight percent, and preferably less than or equal to 0.1
weight percent. For purposes of the present invention, oxide
impurities can be defined as materials which when combined with
each other or with zirconia form phases with melting points much
lower than that of pure zirconia, especially--but not limited
to--soda (Na.sub.2O), silica (SiO.sub.2), and alumina
(Al.sub.2O.sub.3). Other specific concentration ranges of
stabilizers are provided herein and in co-pending and commonly
assigned U.S. patent application Ser. No. 11/520,041, entitled
"HIGH PURITY CERAMIC ABRADABLE COATINGS," U.S. patent application
Ser. No. 11/520,044, entitled "OPTIMIZED HIGH TEMPERATURE THERMAL
BARRIER," and U.S. application Ser. No. 11/520,042, entitled
"OPTIMIZED HIGH PURITY COATING FOR HIGH TEMPERATURE THERMAL CYCLING
APPLICATIONS" each filed on Sep. 13, 2006 and each incorporated
herein by reference.
In accordance with embodiments of the invention, the limits for
known impurities in order to achieve a desirable sintering rate and
therefore increase service lifetime when used as a coating are
about:
TABLE-US-00001 soda (Na.sub.2O) 0.1 weight percent silica
(SiO.sub.2) 0.05 weight percent alumina (Al.sub.2O.sub.3) 0.01
weight percent titania (TiO.sub.2) 0.05 weight percent hematite
(Fe.sub.2O.sub.3) 0.05 weight percent calcia (CaO) 0.05 weight
percent, and magnesia (MgO) 0.05 weight percent.
In a preferred embodiment, the limits for known impurities are
about:
TABLE-US-00002 Na.sub.2O 0.01 weight percent SiO.sub.2 0.01 weight
percent Al.sub.2O.sub.3 0.01 weight percent TiO.sub.2 0.01 weight
percent Fe.sub.2O.sub.3 0.01 weight percent CaO 0.025 weight
percent, and MgO 0.025 weight percent.
The impurity limits in the embodiments above are not indicative
that any or all of the impurities listed will be included in the
material in any amount. The embodiment of the invention may include
zero weight percent of one or more of the above-listed
impurities.
FIG. 3 provides a phase diagram for pure zirconia. (The diagram can
be found, for example, in Ceramic Phase Diagrams vol. 3, figure
04259.) As shown in FIG. 3, pure zirconia exists in three crystal
phases at different temperatures. At very high temperatures
(>2370.degree. C.) the material has a cubic structure. At
intermediate temperatures (1200 to 2372.degree. C.) it has a
tetragonal structure. At relatively lower temperatures (below
1200.degree. C.) the material transforms to the monoclinic
structure. The transformation from tetragonal to monoclinic is
rapid and is accompanied by a 3 to 5 percent volume increase that
causes extensive stress in the material. Thus, pure zirconia cannot
fulfill the coating requirements for high-temperature cycling. The
resulting strain difference between the coating and substrate
caused by the phase transformation results in a stress that is
greater than the bond strength between them, so the coating will
detach.
In accordance with embodiments of the invention, in order to
overcome the volume change caused by the undesired phase
transformation described above, one or more elements are added to
the zirconia to modify the amount of phase transformation that
occurs. The stabilizing elements, which are suitable for changing
the amount and rate of phase transformation that occurs in the
oxide coating, may include the following: scandium, yttrium and the
rare earths, particularly the lanthanides, since they have
solubility in zirconia. Scandium is not typically used due to its
rarity and resulting prohibitive cost. Use of rare earths metals
from the actinide group such as uranium and thorium may be limited
due to their radioactivity. Thus, yttrium is a preferred
stabilizing element.
FIG. 4 provides a standard phase diagram for stabilized zirconia
showing the general alloying trends for the zirconia stabilizers. A
specific diagram for zirconia with yttria as a stabilizer is given
in FIG. 5. (The diagram can be found, for example, in Ceramic Phase
Diagram, vol. Zirconia, figure Zr-157.)
Phase transformation in partially stabilized zirconia may possibly
cause localized stresses that lead to the formation of micron-sized
micro-cracks in the coating upon thermal cycling that cancel out
some of the massive stress caused by coating volume shrinkage.
Thus, these two phenomena of the coating structure--shrinking and
cracking--work against each other and finding a balance between
them will maximize coating lifetime. This mechanism implies then
that the structure of the crack network of the coating is changing
with time as the phase of the ceramic material changes. This
mechanism is required for a thermal barrier or high temperature
abradable coatings to survive thermal cycling.
The addition of a stabilizing element affects two main properties
of the zirconia coating system in a positive manner. First, the
addition of a stabilizer as illustrated in FIG. 4 generally
increases the melting temperature of the zirconia (in the partially
stabilized composition ranges). Second, the addition of a
stabilizer generally decreases the thermal conductivity. Once the
critical composition that has the highest thermal cycling values is
found experimentally for a stabilizer, the stabilizers can be
compared by the melting point at the critical composition.
Rising fuel cost and other factors continue to drive the need for
improved operational efficiency, and thus higher operating
temperatures, of gas turbines. While yttria stabilized zirconia is
the material of choice for stabilization, greater operational
temperatures can be achieved using ytterbia (FIG. 4) for example.
Zirconia partially stabilized by ytterbia provides a better
composition, since it also has one of the lowest thermal
conductivities of the potential stabilizers when alloyed with
zirconia. As the need for higher operating temperatures increases,
a higher coating material cost may be tolerated, so ytterbia
partially stabilized zirconia may become a preferred thermal
barrier or high temperature abradable coating system. Given then
the trade-offs of cost and performance, a combination of both
yttria and ytterbia stabilizers is expected to have optimum
performance to cost ratio.
A blend of two or more partially stabilized high-purity material
compositions may also be used. For example, in another embodiment,
a blended ceramic material for use in high-temperature thermal
barriers is provided. The blended materials include a first
material with a yttria (Y.sub.2O.sub.3) stabilizer, and a balance
of at least one of zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and
combinations thereof, wherein the zirconia (ZrO.sub.2) and/or
hafnia (HfO.sub.2) is partially stabilized by the yttria
stabilizer, and having total impurities less than or equal to 0.15
weight percent, and preferably less than or equal to 0.1 weight
percent. The range of Y.sub.2O.sub.3 stabilizer is about 4-12
weight percent, and preferably 6-9 weight percent. The second
material of the blended material may contain a ytterbia
(Yb.sub.2O.sub.5) stabilizer and a balance of at least one of
zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and combinations
thereof, wherein the zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2)
is partially stabilized by the ytterbia stabilizer, and having
total impurities less than or equal to 0.15 weight percent, and
preferably less than or equal to 0.1 weight percent. The range of
Yb.sub.2O.sub.5 stabilizer is about 4-16 weight percent, and
preferably 10-16 weight percent. In the blended material, the
ytterbia (Yb.sub.2O.sub.5) stabilized zirconia (ZrO.sub.2) and/or
hafnia (HfO.sub.2) fraction may include about 5-50 weight percent
of the total and preferably about 15-30 weight percent of the
total. The yttria stabilized zirconia (ZrO.sub.2) and/or hafnia
(HfO.sub.2) fraction may include about 50-95 weight percent of the
total and preferably about 70-85 weight percent of the total
blend.
In another embodiment the blended material includes a first
material with a ytterbia (Yb.sub.2O.sub.5) stabilizer, and a
balance of at least one of zirconia (ZrO.sub.2) and hafnia
(HfO.sub.2) and combinations thereof, wherein the zirconia
(ZrO.sub.2) and/or hafnia (HfO.sub.2) is partially stabilized by
the ytterbia stabilizer, and having total impurities less than or
equal to 0.15 weight percent, and preferably less than or equal to
0.1 weight percent. The range of Yb.sub.2O.sub.5 stabilizer is
about 4-16 weight percent, and preferably 10-16 weight percent. The
second material of the blended material may contain a stabilizer of
at least one of neodymium (Nd.sub.2O.sub.3), europia
(Eu.sub.2O.sub.5), and combinations thereof and a balance of at
least one of zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and
combinations thereof, wherein the balance is partially stabilized
by the stabilizer, and having total impurities less than or equal
to 0.15 weight percent, and preferably less than or equal to 0.1
weight percent. The range of Nd.sub.2O.sub.3 stabilizer is about
4-20 weight percent, and preferably 8-16 weight percent. The range
of Eu.sub.2O.sub.3 stabilizer is about 4-16 weight percent, and
preferably 10-16 weight percent. The range of the combined
Nd.sub.2O.sub.3 and Eu.sub.2O.sub.3 stabilizer is about 4-16 weight
percent. In the blended material, the ytterbia (Y.sub.2O.sub.3)
stabilized zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) fraction
may include about 5-50 weight percent of the total and preferably
about 15-30 weight percent of the total. The yttria stabilized
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) fraction may include
about 50-95 weight percent of the total and preferably about 70-85
weight percent of the total blend.
In another embodiment of the invention the blended material
includes a first material with a yttria (Y.sub.2O.sub.3)
stabilizer, and a balance of at least one of zirconia (ZrO.sub.2)
and hafnia (HfO.sub.2) and combinations thereof, wherein the
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) is partially
stabilized by the yttria stabilizer, and having total impurities
less than or equal to 0.15 weight percent, and preferably less than
or equal to 0.1 weight percent. The range of Y.sub.2O.sub.3
stabilizer is about 4-12 weight percent, and preferably 6-9 weight
percent. The second material of the blended material may contain a
stabilizer of at least one of neodymium (Nd.sub.2O.sub.3), europia
(Eu.sub.2O.sub.5), and combinations thereof and a balance of at
least one of zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and
combinations thereof, wherein the balance is partially stabilized
by the stabilizer, and having total impurities less than or equal
to 0.15 weight percent, and preferably less than or equal to 0.1
weight percent. The range of Nd.sub.2O.sub.3 stabilizer is about
4-20 weight percent, and preferably 8-16 weight percent. The range
of Eu.sub.2O.sub.3 stabilizer is about 4-16 weight percent, and
preferably 10-16 weight percent. The range of the combined
Nd.sub.2O.sub.3 and Eu.sub.2O.sub.3 stabilizer is about 4-16 weight
percent. In the blended material, the neodymium (Nd.sub.2O.sub.3)
and/or europia (Eu.sub.2O.sub.5) stabilized zirconia (ZrO.sub.2)
and/or hafnia (HfO.sub.2) fraction may include about 5-50 weight
percent of the total and preferably about 15-30 weight percent of
the total. The yttria stabilized zirconia (ZrO.sub.2) and/or hafnia
(HfO.sub.2) fraction may include about 50-95 weight percent of the
total and preferably about 70-85 weight percent of the total
blend.
In a further embodiment of the invention the blended material
includes a blend of at least three materials. The first material
may contain a yttria (Y.sub.2O.sub.3) stabilizer, and a balance of
at least one of zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and
combinations thereof, wherein the zirconia (ZrO.sub.2) and/or
hafnia (HfO.sub.2) is partially stabilized by the yttria
stabilizer, and having total impurities less than or equal to 0.15
weight percent, and preferably less than or equal to 0.1 weight
percent. The range of Y.sub.2O.sub.3 stabilizer is about 4-12
weight percent, and preferably 6-9 weight percent. The second
material of the blend may contain a ytterbia (Yb.sub.2O.sub.5)
stabilizer, and a balance of at least one of zirconia (ZrO.sub.2)
and hafnia (HfO.sub.2) and combinations thereof, wherein the
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) is partially
stabilized by the ytterbia stabilizer, and having total impurities
less than or equal to 0.15 weight percent, and preferably less than
or equal to 0.1 weight percent. The range of Yb.sub.2O.sub.5
stabilizer is about 4-16 weight percent, and preferably 10-16
weight percent. The third material of the blend may contain a
stabilizer of at least one of neodymium (Nd.sub.2O.sub.3), europia
(Eu.sub.2O.sub.5), and combinations thereof and a balance of at
least one of zirconia (ZrO.sub.2) and hafnia (HfO.sub.2) and
combinations thereof, wherein the balance is partially stabilized
by the stabilizer, and having total impurities less than or equal
to 0.15 weight percent, and preferably less than or equal to 0.1
weight percent. The range of Nd.sub.2O.sub.3 stabilizer is about
4-20 weight percent, and preferably 8-16 weight percent. The range
of Eu.sub.2O.sub.3 stabilizer is about 4-16 weight percent, and
preferably 10-16 weight percent. The range of the combined
Nd.sub.2O.sub.3 and Eu.sub.2O.sub.3 stabilizer is about 4-16 weight
percent. In the blended material, the ytterbia (Y.sub.2O.sub.3)
stabilized zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) fraction
may include about 5-45 weight percent of the total, and preferably
about 15-30 weight percent of the total. The neodymium
(Nd.sub.2O.sub.3) and/or europia (Eu.sub.2O.sub.5) stabilized
zirconia (ZrO.sub.2) and/or hafnia (HfO.sub.2) fraction may also
include about 5-45 weight percent of the total and preferably about
15-30 weight percent of the total. The yttria stabilized zirconia
(ZrO.sub.2) and/or hafnia (HfO.sub.2) fraction may include about
10-90 weight percent of the total, and preferably about 30-60
weight percent of the total blend.
Material of embodiments of the present invention can be provided in
a variety of forms for use in thermal spray applications. For
example, the material is supplied in the form of a powder, a slurry
of powder, or a chemical solution of the constituents. If in powder
form, the powder may be in the form of a spray dried powder of the
individual constituents and organic binder, spray dried powder of
the combined individual constituents and organic binder, fused and
crushed powder, agglomerated and sintered powder, plasma densified
material or powder from chemical solution routes. Typical particle
sizes for the powders may vary but typically range between about
5-150 microns when deposited by various thermal spray equipment,
preferably ranging between about 15-125 microns for air plasma
spray and ranging between about 5-30 microns for low pressure
plasma spray.
Typically for thermal spray applications, a polymer or organic
material in powder form can be added to the material blend. Powder
may be in the form of a spray dried powder of the individual
constituents and an organic binder, spray dried powder of the
combined individual constituents and an organic binder, fused and
crushed powder, agglomerated and sintered powder, plasma densified
material or powder from chemical solution routes. The organic
binder may be used to at least partially bond together the
placeholder material and the ceramic material. For high temperature
abradable coatings, the benefit of adding a fugitive phase is that
a higher porosity than is achievable with conventional deposition
methods. The increased porosity aids abradability by introducing
more surfaces to the crack network of the coating, decreasing the
coating elastic modulus and thus promoting controlled material
removal. Thus, according to an embodiment of the invention, a
coating material may have about 70 to 99 weight percent of an
ultra-pure ceramic material as previously described and about 1-30
weight percent (and preferably 2-15 weight percent) of a
placeholder material. The placeholder material may be an organic
powder material or an inorganic powder material that can be burned
out subsequent to deposition of the coating material.
While exemplary embodiments of the invention have been shown and
described herein, it will be obvious to those skilled in the art
that such embodiments are provided by way of example only. Numerous
insubstantial variations, changes, and substitutions will now be
apparent to those skilled in the art without departing from the
scope of the invention disclosed herein by the Applicants.
Accordingly, it is intended that the invention be limited only by
the spirit and scope of the claims, as they will be allowed.
* * * * *
References